Method and apparatus for clamping a substrate in a high pressure processing system

ABSTRACT

Pressure biased wafer holding of a semiconductor wafer is provided for use in high pressure processing. The use of vacuum chucking for holding a semiconductor wafer during processing is applied to high pressure systems. Adverse effects of high pressure biases are prevented by a valve arrangement that reduces or limits the holding load on a wafer. Check valves and on-off valves connected to input and output lines to the chamber bias fluid applied to a wafer supporting platen to vary the backside pressure so that the excess of frontside pressure versus backside pressure on the wafer is kept within an effective clamping range without excessive force being applied to the wafer. Use of fluid-mechanical techniques is maximized in certain described embodiments to avoid disadvantages of electronic control systems.

FIELD OF THE INVENTION

The present invention relates to a method and system for clamping asubstrate in a high pressure processing system and, more particularly,in a supercritical processing system.

BACKGROUND OF THE INVENTION

During the fabrication of semiconductor devices for integrated circuits(ICs), a sequence of material processing steps, including both patternetching and deposition processes, are performed, whereby material isremoved from or added to a substrate surface, respectively. During, forinstance, pattern etching, a pattern formed in a mask layer ofradiation-sensitive material, such as photoresist, using for examplephotolithography, is transferred to an underlying thin material filmusing a combination of physical and chemical processes to facilitate theselective removal of the underlying material film relative to the masklayer.

Thereafter, the remaining radiation-sensitive material, or photoresist,and post-etch residue, such as hardened photoresist and other etchresidues, are removed using one or more cleaning processes.Conventionally, these residues are removed by performing plasma ashingin an oxygen plasma, followed by wet cleaning through immersion of thesubstrate in a liquid bath of stripper chemicals.

Until recently, dry plasma ashing and wet cleaning were found to besufficient for removing residue and contaminants accumulated duringsemiconductor processing. However, recent advancements for ICs include areduction in the critical dimension for etched features below a featuredimension acceptable for wet cleaning, such as a feature dimension belowapproximately 45 to 65 nanometers (nm). Moreover, the advent of newmaterials, such as low dielectric constant (low-k) materials, limits theuse of plasma ashing due to their susceptibility to damage during plasmaexposure.

At present, interest has developed for the replacement of dry plasmaashing and wet cleaning. One interest includes the development of drycleaning systems utilizing a supercritical fluid as a carrier for asolvent, or other residue removing composition. The use of supercriticalcarbon dioxide, for example, in processing semiconductor wafers has beenshown in the art.

Certain challenges occur when attempting to process silicon wafers underhigh pressure. One such issue is how to hold the wafer in place duringprocessing. It has been shown that a wafer can be supported at discretelocations around its edge, with high pressure supercritical carbondioxide (SCCO2) surrounding the entire wafer.

A different approach is to hold the wafer down on a platen using vacuumor reduced pressure from the top surface of the wafer, which has alsobeen shown. In such a case, bias in pressure keeps the wafer in placeduring processing, which may include violent events such as suddendecompressions, high surface velocity jets for cleaning, etc. One of thesignificant drawbacks of vacuum holding is the restraining of the waferagainst the platen. With such a large surface area of 300 millimeter(mm) wafers, for example, the exposed area of the platen, is subjectedto loads that can exceed half a million pounds. Even very thick steelsplatens will deflect under this kind of load. Typical pressuresencountered in SCCO2 processing are a minimum of 1,031 psi, but 3,000psi is not uncommon, and upwards of 10,000 psi has been reported in theliterature.

If a wafer is held against a platen, typically of stainless steel, theresulting static pressure load can force the wafer against the platen,which can cause damage to the backside of the wafer. Particulates thatmay be present can then get embedded into the platen or into thebackside of the wafer. This can cause irreparable harm to the wafer forsubsequent process steps.

Another effect of these high forces is the flexing of the platen underthe pressure load. As the pressure increases, the wafer becomesrestrained against the platen. As pressure continues to increase, theplaten can bow due to the load. The wafer may or may not be able tofollow the new shape that the platen is forced into due to the pressureload. Once the pressure is released or reduced, the wafer must againreadjust for the change in shape of the platen. If multiple pressurecycles are applied, this effect can be repeated many times on a singlewafer.

Results of this flexing can break wafers, because they are brittle andfragile and cannot elastically deform like stainless steel. It can alsocause a grinding or fretting effect between the wafer and the platen,due to the high forces and small displacements which take place. Thiscan create metal or silicon particles to be interspersed between thewafer and platen, which in turn can damage the current wafer, and bepresent on the platen to damage subsequent wafers that are processed.

The magnitude of this flexing may be considered trivial under ordinaryindustrial circumstances. Unfortunately with semiconductor wafers,flexing of less than 0.0010 inches, or even as little as 0.0005 inches,have been shown to cause significant damage to wafers, or waferbreakage.

At present, the inventors have recognized that if the force holding thewafer to the platen is reduced, the wafer can slip in relation to theplaten, and the likelihood of breakage can be reduced. If the holdingforce is reduced even further in magnitude, then wear can also beeliminated because there would not be enough frictional force to createwear or particles.

Misalignment of features on the wafer platen, or poor flatness of theplaten surface can also result in wafer breakage if the holding load ishigh. If the wafer is required to span over holes or slots in theplaten, then the wafer becomes a “bridge” with the entire pressure loadbearing down on an unsupported region of thin silicon. It doesn't take avery large span to break a wafer when subjected to 3,000 psi or higherpressures.

Accordingly, there is a need to overcome the above described problems.

SUMMARY OF THE INVENTION

According to certain principles of the present invention, a processingsystem is provided which comprises a processing chamber configured totreat said substrate therein with a high pressure fluid; a platencoupled to said processing chamber and configured to support saidsubstrate, a fluid supply system, a fluid flow system coupled to saidfluid supply system and said chamber and configured to flow said fluidthrough said processing chamber over said substrate, and a chuck coupledto said platen and configured to hold said substrate against said platenby a pressure gradient between said high pressure fluid and said platen,wherein said chuck includes means responsive to the pressure of saidfluid in said chamber for limiting the magnitude of said pressuregradient.

According to other principles of the present invention, a vacuum chuckassembly is provided comprising a platen having a wafer supportingsurface and configured to support said substrate on said surface forhigh pressure fluid processing, one or more fluid channels in saidplaten coupled to said wafer supporting surface, a clamping fluidcontrol system including a clamping fluid line, a firstpressure-limiting valve, a second pressure-limiting valve and a thirdpressure-limiting valve; said clamping fluid line being coupled to saidchannels, coupled to the outlet of a first pressure-limiting valve thatis operable to maintain the pressure in said clamping fluid line to notless than a first maximum pressure gradient less than the pressure insaid chamber, and coupled to the inlet of a second pressure-limitingvalve that is operable to maintain the pressure in said clamping fluidline to not more than a second maximum pressure gradient more than thepressure to an exhaust line that is coupled to said chamber; said thirdpressure-limiting valve having an inlet coupled to said chamber, havingan outlet coupled to said exhaust line, and being operable to maintainthe pressure in said exhaust line at a pressure that is not less than athird maximum pressure gradient less than the pressure in said chamber;said third maximum pressure gradient being greater than said secondmaximum pressure gradient.

According to other principles of the present invention, a method ofcontrolling fluid clamping pressure to the backside of a substrate on aplaten of a pressure biased wafer holder in a high pressure processingchamber is provided that comprises filling the processing chamber withprocessing fluid to a high processing pressure and applying a clampingfluid to a backside of a substrate on a platen in said processingchamber at a backside pressure that is responsive to the frontsidepressure exerted by said fluid on said substrate, with the backsidepressure being less than the frontside pressure by not more than amaximum clamping pressure gradient.

These and other objectives and advantages of the present invention areset forth in the detailed description of the exemplary embodimentsbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a simplified schematic representation of one embodiment of aprocessing system according to principles of the present invention;

FIG. 1A is a diagram of a portion of FIG. 1 representing the processingsystem at idle, prior to pressurization of the chamber, with the chamberat 0 psig (atmospheric pressure);

FIG. 1B is a diagram similar to FIG. 1A but representing the processingsystem as the chamber is beginning to fill, with fluid therein at 100psig;

FIG. 1C is a diagram similar to FIG. 1B but representing the processingsystem as the chamber continues to fill, with fluid in the chamber at300 psig;

FIG. 1D is a diagram similar to FIG. 1C but representing the processingsystem with the chamber at a processing pressure of 3,000 psig;

FIG. 1E is a diagram similar to FIG. 1D but representing the processingsystem as the chamber is beginning to vent, with fluid in the chamber at1,500 psig;

FIG. 1F is a diagram similar to FIG. 1E but representing the processingsystem as the chamber continues to vent, with fluid in the chamber at100 psig;

FIG. 1G is a diagram similar to FIG. 1F but representing the processingsystem as the chamber has been vented to atmospheric pressure, or 0psig; and

FIG. 1H is a diagram similar to FIG. 1G but representing the processingsystem after the chamber has been vented and the platen isback-pressurized for removal of the wafer.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

In the following description, to facilitate a thorough understanding ofthe invention and for purposes of explanation and not limitation,specific details are set forth, such as a particular geometry of theprocessing system and various descriptions of the system components.However, it should be understood that the invention may be practicedwith other embodiments that depart from these specific details.

Referring now to the drawings, wherein like reference numerals designateidentical or corresponding parts throughout the several views, FIG. 1illustrates a processing system 100 according to an embodiment of theinvention. In the illustrated embodiment, processing system 100 isconfigured to treat a substrate 105 with a high pressure fluid, such asa fluid in a supercritical state, with or without other additives, suchas process chemistry. The processing system 100 comprises processingelements that include a processing chamber 110, a fluid flow system 120,a process chemistry supply system 130, a high pressure fluid supplysystem 140, and a controller 150, all of which are configured to processsubstrate 105. The controller 150 can be coupled to the processingchamber 110, the fluid flow system 120, the process chemistry supplysystem 130, and the high pressure fluid supply system 140.

Alternately, or in addition, controller 150 can be coupled to a one ormore additional controllers/computers (not shown), and controller 150can obtain setup and/or configuration information from an additionalcontroller/computer.

In FIG. 1, singular processing elements (110, 120, 130, 140, and 150)are shown, but this is not required for the invention. The processingsystem 100 can comprise any number of processing elements having anynumber of controllers associated with them in addition to independentprocessing elements.

The controller 150 can be used to configure any number of processingelements (110, 120, 130, and 140), and the controller 150 can collect,provide, process, store, and display data from processing elements. Thecontroller 150 can comprise a number of applications for controlling oneor more of the processing elements. For example, controller 150 caninclude a graphic user interface (GUI) component (not shown) that canprovide easy to use interfaces that enable a user to monitor and/orcontrol one or more processing elements.

Referring still to FIG. 1, the fluid flow system 120 is configured toflow fluid and chemistry from the supplies 130 and 140 through theprocessing chamber 110. The fluid flow system 120 is illustrated as arecirculation system through which the fluid and chemistry recirculatefrom, and back to, the processing chamber 110 via primary flow line 122.This recirculation is most likely to be the preferred configuration formany applications, but this is not necessary to the invention. Fluids,particularly inexpensive fluids, can be passed through the processingchamber 110 once and then discarded, which might be more efficient thanreconditioning them for re-entry into the processing chamber.Accordingly, while the fluid flow system or recirculation system 120 isdescribed as a recirculating system in the exemplary embodiments, anon-recirculating system may, in some cases, be substituted. This fluidflow system 120 can include one or more valves (not shown) forregulating the flow of a processing solution through the fluid flowsystem 120 and through the processing chamber 110. The fluid flow system120 can comprise any number of back-flow valves, filters, pumps, and/orheaters (not shown) for maintaining a specified temperature, pressure orboth for the processing solution and for flowing the process solutionthrough the fluid flow system 120 and through the processing chamber110. Furthermore, any one of the many components provided within thefluid flow system 120 may be heated to a temperature consistent with thespecified process temperature.

Some components, such as a fluid flow or recirculation pump, may requirecooling in order to permit proper functioning. For example, somecommercially available pumps, having specifications required forprocessing performance at high pressure and cleanliness duringsupercritical processing, comprise components that are limited intemperature. Therefore, as the temperature of the fluid and structureare elevated, cooling of the pump is required to maintain itsfunctionality. Fluid flow system 120 for circulating or otherwiseflowing the supercritical fluid through processing chamber 110 cancomprise the primary flow line 122 coupled to high pressure processingsystem 100, and configured to supply the supercritical fluid at a fluidtemperature equal to or greater than 40 degrees C. to the high pressureprocessing system 100, and a high temperature pump (not shown) coupledto the primary flow line 122. The high temperature pump can beconfigured to move the supercritical fluid through the primary flow line122 to the processing chamber 110, wherein the high temperature pumpcomprises a coolant inlet configured to receive a coolant and a coolantoutlet configured to discharge the coolant. A heat exchanger (not shown)coupled to the coolant inlet can be configured to lower a coolanttemperature of the coolant to a temperature less than or equal to thefluid temperature of the supercritical fluid. Details regarding pumpdesign are provided in co-pending U.S. patent application Ser. No.10/987,066, entitled “Method and System for Cooling a Pump”; the entirecontent of which is herein incorporated by reference in its entirety.

Referring again to FIG. 1, the processing system 100 can comprise highpressure fluid supply system 140. The high pressure fluid supply system140 can be coupled to the fluid flow system 120, but this is notrequired. In alternate embodiments, high pressure fluid supply system140 can be configured differently and coupled differently. For example,the fluid supply system 140 can be coupled directly to the processingchamber 110. The high pressure fluid supply system 140 can include asupercritical fluid supply system. A supercritical fluid as referred toherein is a fluid that is in a supercritical state, which is that statethat exists when the fluid is maintained at or above the criticalpressure and at or above the critical temperature on its phase diagram.In such a supercritical state, the fluid possesses certain properties,one of which is the substantial absence of surface tension. Accordingly,a supercritical fluid supply system, as referred to herein, is one thatdelivers to a processing chamber a fluid that assumes a supercriticalstate at the pressure and temperature at which the processing chamber isbeing controlled. Furthermore, it is only necessary that at least at ornear the critical point the fluid is in substantially a supercriticalstate at which its properties are sufficient, and exist long enough, torealize their advantages in the process being performed. Carbon dioxide,for example, is a supercritical fluid when maintained at or above apressure of about 1,070 psi at a temperature of 31 degrees C. This stateof the fluid in the processing chamber may be maintained by operatingthe processing chamber at 2,000 to 10,000 psi at a temperature ofapproximately 40 degrees C. or greater.

As described above, the fluid supply system 140 can include asupercritical fluid supply system, which can be a carbon dioxide supplysystem. For example, the fluid supply system 140 can be configured tointroduce a high pressure fluid having a pressure substantially near thecritical pressure for the fluid. Additionally, the fluid supply system140 can be configured to introduce a supercritical fluid, such as carbondioxide in a supercritical state. Additionally, for example, the fluidsupply system 140 can be configured to introduce a supercritical fluid,such as supercritical carbon dioxide, at a pressure ranging fromapproximately the critical pressure of carbon dioxide to 10,000 psi.Examples of other supercritical fluid species useful in the broadpractice of the invention include, but are not limited to, carbondioxide (as described above), oxygen, argon, krypton, xenon, ammonia,methane, methanol, dimethyl ketone, hydrogen, water, and sulfurhexafluoride. The fluid supply system can, for example, comprise acarbon dioxide source (not shown) and a plurality of flow controlelements (not shown) for generating a supercritical fluid. For example,the carbon dioxide source can include a CO2 feed system, and the flowcontrol elements can include supply lines, valves, filters, pumps, andheaters. The fluid supply system 140 can comprise an inlet valve (notshown) that is configured to open and close to allow or prevent thestream of supercritical carbon dioxide from flowing into the processingchamber 110. For example, controller 150 can be used to determine fluidparameters such as pressure, temperature, process time, and flow rate.

Referring still to FIG. 1, the process chemistry supply system 130 iscoupled to the recirculation system 120, but this is not required forthe invention. In alternate embodiments, the process chemistry supplysystem 130 can be configured differently, and can be coupled todifferent elements in the processing system 100. The process chemistryis introduced by the process chemistry supply system 130 into the fluidintroduced by the fluid supply system 140 at ratios that vary with thesubstrate properties, the chemistry being used and the process beingperformed in the processing chamber 110. Usually the ratio is roughly 1to 15 percent by volume in systems where the chamber, recirculationsystem and associated plumbing have a volume of about one liter. Thisamounts to about 10 to 150 milliliters of additive in most cases. Theratio may be higher or lower.

The process chemistry supply system 130 can be configured to introduceone or more of the following process compositions, but not limited to:cleaning compositions for removing contaminants, residues, hardenedresidues, photoresist, hardened photoresist, post-etch residue, post-ashresidue, post chemical-mechanical polishing (CMP) residue,post-polishing residue, or post-implant residue, or any combinationthereof; cleaning compositions for removing particulate; dryingcompositions for drying thin films, porous thin films, porous lowdielectric constant materials, or air-gap dielectrics, or anycombination thereof; film-forming compositions for preparing dielectricthin films, metal thin films, or any combination thereof; healingcompositions for restoring the dielectric constant of low dielectricconstant (low-k) films; sealing compositions for sealing porous films;or any combination thereof. Additionally, the process chemistry supplysystem 130 can be configured to introduce solvents, co-solvents,surfactants, etchants, acids, bases, chelators, oxidizers, film-formingprecursors, or reducing agents, or any combination thereof.

The process chemistry supply system 130 can be configured to introduceN-methyl pyrrolidone (NMP), diglycol amine, hydroxyl amine, di-isopropylamine, tri-isoprpyl amine, tertiary amines, catechol, ammonium fluoride,ammonium bifluoride, methylacetoacetamide, ozone, propylene glycolmonoethyl ether acetate, acetylacetone, dibasic esters, ethyl lactate,CHF3, BF3, HF, other fluorine containing chemicals, or any mixturethereof. Other chemicals such as organic solvents may be utilizedindependently or in conjunction with the above chemicals to removeorganic materials. The organic solvents may include, for example, analcohol, ether, and/or glycol, such as acetone, diacetone alcohol,dimethyl sulfoxide (DMSO), ethylene glycol, methanol, ethanol, propanol,or isopropanol (IPA). For further details, see U.S. Pat. No. 6,306,564,filed May 27, 1998, and titled “Removal of Resist or Residue fromSemiconductors Using Supercritical Carbon Dioxide”, and U.S. Pat. No.6,509,141, filed Sep. 3, 1999, and titled “Removal of Photoresist andPhotoresist Residue from Semiconductors Using Supercritical Carbondioxide Process,” both incorporated by reference herein.

Additionally, the process chemistry supply system 130 can comprise acleaning chemistry assembly (not shown) for providing cleaning chemistryfor generating supercritical cleaning solutions within the processingchamber. The cleaning chemistry can include peroxides and a fluoridesource. For example, the peroxides can include hydrogen peroxide,benzoyl peroxide, or any other suitable peroxide, and the fluoridesources can include fluoride salts (such as ammonium fluoride salts),hydrogen fluoride, fluoride adducts (such as organo-ammonium fluorideadducts), and combinations thereof. Further details of fluoride sourcesand methods of generating supercritical processing solutions withfluoride sources are described in U.S. patent application Ser. No.10/442,557, filed May 20, 2003, and titled “Tetra-Organic AmmoniumFluoride and HF in Supercritical Fluid for Photoresist and ResidueRemoval”, and U.S. patent application Ser. No. 10/321,341, filed Dec.16, 2002, and titled “Fluoride in Supercritical Fluid for PhotoresistPolymer and Residue Removal,” both incorporated by reference herein.

Furthermore, the process chemistry supply system 130 can be configuredto introduce chelating agents, complexing agents and other oxidants,organic and inorganic acids that can be introduced into thesupercritical fluid solution with one or more carrier solvents, such asN,N-dimethylacetamide (DMAc), gamma-butyrolactone (BLO), dimethylsulfoxide (DMSO), ethylene carbonate (EC), N-methyl pyrrolidone (NMP),dimethylpiperidone, propylene carbonate, and alcohols (such a methanol,ethanol and 2-propanol).

Moreover, the process chemistry supply system 130 can comprise a rinsingchemistry assembly (not shown) for providing rinsing chemistry forgenerating supercritical rinsing solutions within the processingchamber. The rinsing chemistry can include one or more organic solventsincluding, but not limited to, alcohols and ketone. In one embodiment,the rinsing chemistry can comprise sulfolane, also known asthiocyclopentane-1,1-dioxide, (cyclo)tetramethylene sulphone and2,3,4,5-tetrahydrothiophene-1,1-dioxide, which can be purchased from anumber of venders, such as Degussa Stanlow Limited, Lake Court, HursleyWinchester SO21 2LD UK.

Furthermore, the process chemistry supply system 130 can be configuredto introduce treating chemistry for curing, cleaning, healing (orrestoring the dielectric constant of low-k materials), or sealing, orany combination thereof, or for applying low dielectric constant films(porous or non-porous). The chemistry can include hexamethyldisilazane(HMDS), chlorotrimethylsilane (TMCS), trichloromethylsilane (TCMS),dimethylsilyldiethylamine (DMSDEA), tetramethyldisilazane (TMDS),trimethylsilyldimethylamine (TMSDMA), dimethylsilyldimethylamine(DMSDMA), trimethylsilyldiethylamine (TMSDEA), bistrimethylsilyl urea(BTSU), bis(dimethylamino)methyl silane (B[DMA]MS), bis(dimethylamino)dimethyl silane (B [DMA]DS), HMCTS,dimethylaminopentamethyldisilane (DMAPMDS),dimethylaminodimethyldisilane (DMADMDS), disila-aza-cyclopentane(TDACP), disila-oza-cyclopentane (TDOCP), methyltrimethoxysilane(MTMOS), vinyltrimethoxysilane (VTMOS), or trimethylsilylimidazole(TMSI). Additionally, the chemistry may includeN-tert-butyl-1,1-dimethyl-1-(2,3,4,5-tetramethyl-2,4-cyclopentadiene-1-yl)silanamine,1,3-diphenyl-1,1,3,3-tetramethyldisilazane, ortert-butylchlorodiphenylsilane. For further details, see U.S. patentapplication Ser. No. 10/682,196, filed Oct. 10, 2003, and titled “Methodand System for Treating a Dielectric Film,” and U.S. patent applicationSer. No. 10/379,984, filed Mar. 4, 2003, and titled “Method ofPassivating Low Dielectric Materials in Wafer Processing,” bothincorporated by reference herein.

Additionally, the process chemistry supply system 130 can be configuredto introduce peroxides during, for instance, cleaning processes. Theperoxides can include organic peroxides, or inorganic peroxides, or acombination thereof. For example, organic peroxides can include2-butanone peroxide; 2,4-pentanedione peroxide; peracetic acid; t-butylhydroperoxide; benzoyl peroxide; or m-chloroperbenzoic acid (mCPBA).Other peroxides can include hydrogen peroxide.

The processing chamber 110 can be configured to process substrate 105 byexposing the substrate 105 to fluid from the fluid supply system 140, orprocess chemistry from the process chemistry supply system 130, or acombination thereof in a processing space 112. Additionally, processingchamber 110 can include an upper chamber assembly 114, and a lowerchamber assembly 115.

The upper chamber assembly 114 can comprise a heater (not shown) forheating the processing chamber 110, the substrate 105, or the processingfluid, or a combination of two or more thereof. Alternately, a heater isnot required. Additionally, the upper chamber assembly 114 can includeflow components for flowing a processing fluid through the processingchamber 110. In one embodiment, the high pressure fluid is introduced tothe processing chamber 110 through a ceiling formed in the upper chamberassembly 112 and located above substrate 105 through one or more inletslocated above a substantially center portion of substrate 105. The highpressure fluid flows radially outward across an upper surface ofsubstrate 105 beyond a peripheral edge of substrate 105, and dischargesthrough one or more outlets, wherein the spacing between the uppersurface of substrate 105 and the ceiling decreases with radial positionfrom proximate the substantially center portion of substrate 105 to theperipheral edge of substrate 105.

The lower chamber assembly 115 can include a platen 116 configured tosupport substrate 105 and a drive mechanism 118 for translating theplaten 116 in order to load and unload substrate 105, and sealing lowerchamber assembly 115 with upper chamber assembly 114. The platen 116 canalso be configured to heat or cool the substrate 105 before, during,and/or after processing the substrate 105. For example, the platen 116can include one or more heater rods configured to elevate thetemperature of the platen to approximately 31 degrees C. or greater.Additionally, the lower assembly 115 can include a lift pin assembly fordisplacing the substrate 105 from the upper surface of the platen 116during substrate loading and unloading.

Additionally, controller 150 includes a temperature control systemcoupled to one or more of the processing chamber 110, the fluid flowsystem 120 (or recirculation system), the platen 116, the high pressurefluid supply system 140, or the process chemistry supply system 130. Thetemperature control system is coupled to heating elements embedded inone or more of these systems, and configured to elevate the temperatureof the supercritical fluid to approximately 31 degrees C. or greater.The heating elements can, for example, include resistive heatingelements.

A transfer system (not shown) can be used to move a substrate into andout of the processing chamber 110 through a slot (not shown). In oneexample, the slot can be opened and closed by moving the platen 116, andin another example, the slot can be controlled using an on-off valve(not shown).

The substrate can include semiconductor material, metallic material,dielectric material, ceramic material, or polymer material, or acombination of two or more thereof. The semiconductor material caninclude Si, Ge, Si/Ge, or GaAs. The metallic material can include Cu,Al, Ni, Pb, Ti, and/or Ta. The dielectric material can include silica,silicon dioxide, quartz, aluminum oxide, sapphire, low dielectricconstant materials, TEFLON®, and/or polyimide. The ceramic material caninclude aluminum oxide, silicon carbide, etc.

The processing system 100 can further comprise an exhaust controlsystem. The exhaust control system can be coupled to the processingchamber 110, but this is not required. In alternate embodiments, theexhaust control system can be configured differently and coupleddifferently. The exhaust control system can include an exhaust gascollection vessel (not shown) and can be used to remove contaminantsfrom the processing fluid. Such exhaust control system can be used as analternative to the recirculation system 120 that is provided to recyclethe processing fluid.

The processing system 100 can also comprise a pressure control system(not shown). The pressure control system can be coupled to theprocessing chamber 110, but this is not required. In alternateembodiments, the pressure control system can be configured differentlyand coupled differently. The pressure control system can include one ormore pressure valves (not shown) for exhausting the processing chamber110 and/or for regulating the pressure within the processing chamber110. Alternately, the pressure control system can also include one ormore pumps (not shown). For example, one pump may be used to increasethe pressure within the processing chamber, and another pump may be usedto evacuate the processing chamber 110. In another embodiment, thepressure control system can comprise seals for sealing the processingchamber. In addition, the pressure control system can comprise anelevator for raising and lowering the substrate 105 and/or the platen116.

The platen 116 includes a vacuum chuck for clamping the wafer to theplaten. The vacuum chuck is coupled to a vacuum clamping system 160which maintains a controlled clamping pressure differential for holdingthe wafer to the platen 116.

FIGS. 1A-1H are schematic diagrams showing the vacuum clamping system160 in various stages of operation, including the valve and check valvescheme that creates a pressure bias across the wafer under allprocessing conditions. The system 160 includes a chamber exit valveassembly 170 that controls flow of the processing fluid from theprocessing space 112 within the chamber 110 into line 120, an entryvalve assembly that controls the flow of processing fluid from the line120 into the processing space 112 within the chamber 110, and a platenpressure regulating assembly 190 that controls the pressure of gas underthe wafer 105 on the platen 116 in relation to the pressure in theprocessing space 112 within the chamber 110.

FIGS. 1A through 1H show the sequence, in order, of processing a singlewafer 105. The pressures picked are for illustration purposes, and canbe of any range of pressures. The relationship of the opening values ofthe check valves produces the operation scheme of this invention.

FIG. 1A shows the tool 100 in an idle configuration. A wafer 105 hasbeen placed in the processing chamber 110. Gages 102, 172, 182 and 192are shown on each leg of the tool 100 for illustrating pressures in eachleg. Additional valving and components are anticipated, such as safetyrelief devices, but are not shown for simplicity of illustration. Theyare not critical to the basis of this invention, and have been omitted.

As shown in FIG. 1A, chamber 110 includes an inlet port 106 and anexhaust port 108 for flow of the processing fluid through the chamber110. Clean, fresh processing fluid enters the chamber 110 through theinlet port 106 from a fluid entry line 124 and fluid carrying materialcleaned or otherwise removed from the substrate 105 exits the chamber110 through exhaust port 108 into exhaust line 126. The fluid may or maynot be recirculated from line 126 to line 124 through system 120, viathe fluid flow line 122, which cleans and reconditions the fluid.

The chamber exit valve assembly 170 in line 126 includes a check valve174 and on-off valve 176 connected in series in line 126. The valveassembly 170 includes a bypass valve 178 in parallel to the check andon-off valves 174 and 176. A control fluid vent tap 179 is located inline 126 between the check valve 174 and the on-off valve 176. Thechamber inlet valve assembly 180 in line 124 includes an on-off valve184 in line 124. The assembly 180 may optionally include an on-off valve186 connected in line 124 between the valve 184 and the chamber inletport 106. A control fluid supply tap 189 is located in line 124 betweenthe on-off valves 184 and 186.

The platen pressure regulating assembly 190 includes a control fluidline 191 connected between the vent tap 179 and the supply tap 189. Incontrol fluid line 191 are connected an exit check valve 193 and aninlet check valve 194. Gage 172 is connected to a portion 177 of theline 191 between the tap 179 and valve 193 to indicate the pressure outof the regulating assembly 190, and the gage 182 is connected to line191 between the valve 194 and the supply tap 189 to indicate thepressure into the regulating assembly 190. Vacuum ports 117 in theplaten 116 beneath the wafer 105 are maintained at a clamping pressurethat, while not necessarily at a vacuum relative to standard atmosphericpressure, are nonetheless at a pressure below the pressure of theprocessing space 112 within the chamber 110 during operation. The ports117 are connected to a center section 199 of control line 191 betweencheck valves 193 and 194. The gage 192 is connected to this line toindicate the platen clamping pressure. Gas into and out of the controlline 191 at this central portion 199 flows through on-off valve 195, towhich is a vacuum pump 196. To the line between the valve 195 and thepump 196 is connected a blow off gas supply 197 through an on-off valve198.

FIG. 1A illustrates the system in the idle state in which valve 184 isclosed. At this time, upstream pressure might be 3,000 psi, for example.Valve 186, which is open, is optional and can be used to isolate thechamber volume from the inlet line and to prevent backflow andcontamination of the inlet line when the system is disconnected, forexample to add an additional component to the process layout. At thistime, the chamber 110 is at atmospheric (atm) pressure, as measured atgage 102. The wafer 105 is depicted over the vacuum ports 117 of theplaten 116. The ports 117, while positioned to suck the wafer downagainst the platen, are nonetheless at atmospheric pressure at start up.

The check valve 174 is a spring check valve having a spring pressurechosen at 100 psi for this example. It operates as a pressure reliefvalve that permits fluid to flow through it only in a forward directionand only when a pressure gradient of at least 100 psi is present acrossthe valve in the forward direction. As such, the gas pressure in thechamber must build up to over 100 psi for any of it to flow past thecheck valve 174 and out to the open on-off vent valve 176. Vent on-offvalve 178 is employed to bleed off the chamber pressure that is retainedby the spring rating of the check valve 174 (100 psi) to more fullydepressurize the chamber 110.

Exit check valve 193 is a low pressure check valve and controls clampingpressure during a decompression sequence. A small pressure value ischosen for this check valve (for example, 10 psi). It also operates as apressure relief valve as valve 174 described above. The check valve 193causes the pressure in lines connected to the wafer vacuum ports 117 inthe platen 116 to be, at most, slightly more than 10 psi above that atthe return port 179, which is, at most, slightly more than 100 psi belowthat of the processing space within the chamber 10.

Inlet check valve 194 and the valve 195 isolate the vacuum pump 196.Valve 197 controls very low pressure gas, nitrogen in this example, tobreak any vacuum in the lines and allow the wafer 105 to release fromthe surface of the platen 116. The vacuum pump 196 generates vacuum onthe backside of the wafer 105, when necessary.

FIG. 1B shows the system 100 at the start of a chamber fill sequence.The vacuum pump 196 is operating, and valve 195 is open allowing vacuum,below atmospheric pressure, to be applied to the backside of the wafer105 to hold it in place on the platen 116. Valve 198 is closed. Checkvalve 193 and check valve 194 do not allow flow under this condition. Avacuum level of, for example, only −11 psig, which appears at line 199and at the ports 117 in the platen 116, will be shown at gage 192. Ahigher vacuum is generally not required, although is possible up toapproximately −14.7 psig. The pump 196 and valves 195 and 198 arecontrolled by signals from the controller 150, as are the other valvesand components described below. The gas flowing through line 124 may bea neutral gas such as argon, or nitrogen if the chemistry allows, or maybe a processing fluid in the gaseous state, for example carbon dioxide.

Valve 195 is closed after vacuum has been established on the backside ofthe wafer 105. When pressure begins to increase in inlet line 124, forexample with 100 psig being read at gage 182, and continues throughvalve 186 and into the chamber 110, the difference between topside andbackside pressure on the wafer 105 might then be 100 psi+11 psi, or 111psi for retaining the wafer 105 against the surface of the platen 116.The fluid pressure does not yet flow past the exit check valve 174 andhas not yet filled the line 177 to the low pressure check valve 193.Vent valves 176 and 178 are closed at this time.

FIG. 1C shows a further step during the fill sequence. When the pressurein inlet line 124 exceeds 200 psig, inlet check valve 194, whichoperates as a pressure relief valve, begins to open so that, when 300psig of fill gas has built up past valve 184 and valve 186, as indicatedon gage 182, and into the chamber 110, as indicated on gage 102, inletcheck valve 194 has allowed 100 psig to reach line 199 to ports 117behind the wafer 105, as indicated on gage 192. The holding load on thewafer 105 would then be 300 psi−100 psi, or 200 psi. Exit check valve174 will have allowed 200 psi to flow by, which forces low pressurecheck valve 193 to stay closed, as the pressure on line 177 will begreater than that on line 199, as indicated on gages 172 and 192,respectively.

FIG. 1D shows the filled state of the chamber 110 at maximum oroperating pressure. Valve 184 can now be closed. Optional isolationvalve 186 can also be closed at this time. When 3,000 psig is present inthe fill line 124, as indicated on gage 182, 3,000 psig will also bepresent in the chamber 110, as indicated on gage 102. At this point,fluid from the chamber 110 will have filled the line 126 and filled pastthe exit check valve 174 and line 177 to the low pressure check valve193 to a pressure of 2,900 psig, as indicated at gage 172. Low pressurecheck valve 193 will remain closed, as 2,800 psig will be present inline 199, as indicated on gage 192, which has been filled from line 124through the 200 psi drop of inlet check valve 194. This pressure of2,800 psig is communicated to ports 117 behind the wafer 105, so thatthe total clamping pressure on the wafer 105 is now 3,000 psi−2,800 psi,or 200 psi. This is the same as during the early filling stage when thechamber pressure was at only 300 psig. The value of the inlet checkvalve 194 regulates the pressure bias across the wafer 105 duringchamber fill and filled conditions.

FIG. 1E shows the state of the system 100 during the initial period whenthe chamber 110 is being vented and the pressure of the fluid therein isbeing reduced. The venting to half process pressure of 1,500 psig isshown, as indicated on gage 102 and gage 182. For the venting of thechamber 110, vent valve 176 is opened to allow flow through line 126into line 122 to depressurize the process chamber 110. The line afterthe exit check valve 174 will be at 100 psi less in pressure than thechamber 110, or 1,400 psig as indicated on gage 172, due to the valuechosen for the exit check valve 174. The low pressure check valve 193will hold back that line pressure plus the differential pressure valuedetermined by its spring or setting, which, in the example shown, is 10psi. Therefore, the pressure in the line 199 and in the ports 117 behindthe wafer 105 is 1,400 psi+10 psi, or 1,410 psi, as indicated on gage192. The holding load on the wafer is 1,500 psi−1,410 psi, or 90 psi.This value can be changed by changing the value of the spring of exitcheck valve 174, or by changing the rating on the low pressure checkvalve 193. Note that the inlet check valve 194 will not allow fluid tofill into the line 199 behind the wafer, because the pressure dropbetween line 124 and line 199 is less than the value of the 200 psispring setting of inlet check valve 194.

FIG. 1F shows the system 100 nearly completely depressurized. Only theresidual pressure in the chamber 110 and fill line 124 remains at alevel equal to the spring value setting of exit check valve 174, or 100psig in this example, as valve 176 remains open, but valve 184 can havebeen closed. At 100 psig in chamber 110, no more fluid will flow out ofexhaust port 108 as check valve 174 will close. Atmospheric pressure, orabout 0 psig, can be indicated on gage 172. At this time, the valve 195can start to open to evacuate the line to the backside of the wafer 105and to keep some wafer holding pressure differential on the wafer 105 tohold the wafer 105 to the platen 116. Opening valve 195 when the chamberis at 100 psig, as indicated on gage 102, keeps the wafer holdingpressure initially at 100 psi−10 psi, or still 90 psi, due to thesetting of check valve 193. This holding pressure can be increased byvacuum applied to the backside of the wafer (100 psi+11 psi=11 psi max)by operating pump 196.

FIG. 1G shows the system 100 with the chamber 110 in a fully ventedstate. This is achieved by opening vent valve 178 to bypass exit checkvalve 174 and allowing the pressure in the chamber 110 to drop toatmospheric pressure with the fluid flowing from the chamber 110 to line126. The vacuum pump 196 remains on during this final evacuation so thatthe backside pressure, as indicated on gage 192, remains negativerelative to that of the chamber 110, as indicated on gage 102. Thebackside pressure will, for example, have decreased to −11 psig. Theoptional chamber isolation valve 186, if provided, may or may not beopen. If closed, it can trap the final 100 psig in the line 124; if openor absent, the line 124 will have bled down to atmospheric pressurealong with the chamber 110. The wafer holding pressure will now be justthe difference between atmospheric pressure and the level of vacuumproduced by the vacuum pump 196. In this example, the holding pressuredifferential is 11 psi.

FIG. 1H shows the status of the system 100 during wafer removal. Due tothe high polish on the wafer 105 and the wafer holding surface of theplaten 116, a wafer 105 might tend to stick to the surface of the platen116 and be difficult to lift off. A gentle flow of gas from the ports117 in the platen 116 may be used to break the vacuum seal and allow thewafer 105 to be lifted off the surface of the platen 116 by lift pins orother mechanisms (not shown). For this, the vacuum pump 196 is turnedoff and a blow off valve, valve 198 is opened, with valve 195 remainingopen. This provides a path applying gas, such as nitrogen or another gascompatible with the process, to flow from a supply at low pressure, forexample 2 psig, to the ports 117 at the backside of the wafer 105.

It is anticipated that the process implementing the pressure sequencesdescribed above for wafer backside pressure control can be attained bycomplex electronic pressure regulation with hardware/softwareinterfaces. Use of the hardware features described above, however,provides advantages by eliminating drawbacks of an electronic system,which include the cost, which can easily be 10 times higher, the timeand effort required for setup and calibration, as well as thereliability issues with electronic components and software, which maymake such components impractical to implement such a system.

While the mechanical embodiments described above include primarilyvacuum chucking systems that apply the processing fluid itself behindthe wafer on the platen, the processing fluid can instead be used as apilot or control fluid that operates one or more pilot controlled fluidvalves to communicate another fluid, for example an inert gas, behindthe wafer.

Further, the processing chamber 110 can alternatively be configured asdescribed in pending U.S. patent application Ser. No. 09/912,844 (U.S.Patent Application Publication No. 2002/0046707 A1), entitled “Highpressure processing chamber for semiconductor substrates”, filed on Jul.24, 2001, which is incorporated herein by reference in its entirety.

Pressure biased wafer holding of a semiconductor wafer has beendescribed above for use in high pressure processing while preventing theadverse effects of high pressure biases. Controller controlled pressureto the backside of the supported substrate can be used to confine thepressure gradient that holds a wafer to the platen to a specified rangebetween a maximum and minimum clamping pressure. A valve arrangementthat reduces or limits the holding load on a wafer, as described in theillustrated embodiments, is particularly advantageous. Check valves andon-off valves, connected to input and output lines to the chamber, biasfluid applied to a wafer supporting platen to vary the backside pressureso that the excess of frontside pressure versus backside pressure on thewafer is kept within an effective clamping range without excessive forcebeing applied across the wafer. Use of fluid-mechanical techniques ismaximized in certain described embodiments to provide particularreliability and other advantages over electronic control systems.

While the illustrated embodiments include valves located in fluid flowlines outside of the processing chamber, many of the advantages of afluid mechanical system can be provided by substituting fluid flow pathsin the platen itself or otherwise in the chamber that provide forattenuated flow of fluid from the chamber to behind substrate on theplaten so as to develop a clamping pressure gradient within the desiredpressure range.

Although only certain exemplary embodiments of this invention have beendescribed in detail above, those skilled in the art will readilyappreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of this invention. Accordingly, all such modifications areintended to be included within the scope of this invention.

1. A processing system for treating a substrate comprising: a processingchamber configured to treat said substrate therein with a high pressurefluid; a platen coupled to said processing chamber and configured tosupport said substrate; a fluid supply system; a fluid flow systemcoupled to said fluid supply system and said chamber and configured toflow said fluid through said processing chamber over said substrate; achuck coupled to said platen and configured to hold said substrateagainst said platen by a pressure gradient between said high pressurefluid and said platen; and said chuck including means responsive to thepressure of said fluid in said chamber for limiting the magnitude ofsaid pressure gradient.
 2. The processing system of claim 1, whereinsaid means for limiting includes means for limiting said pressuregradient to less than the pressure difference between the pressure ofsaid fluid in said chamber and atmosphere.
 3. The processing system ofclaim 1, wherein said means for limiting includes means for increasingthe pressure of fluid between the substrate and the platen in accordancewith increases of the pressure of fluid in the chamber.
 4. Theprocessing system of claim 1, wherein said means for limiting includesone or more pressure regulated check valves connected between ports tothe backside of the platen to processing fluid inlet or outlet ports ofthe chamber.
 5. The processing system of claim 4, wherein said one ormore check valves have bias pressure settings corresponding to themagnitude of said pressure gradient.
 6. The processing system of claim4, further comprising controller operated on-off valves having open andclosed positions and coupled to said check valves and said chamber. 7.The processing system of claim 1, wherein a temperature of said highpressure fluid ranges from approximately 31 degrees C. to 350 degrees C.8. The processing system of claim 1, wherein a pressure of said highpressure fluid ranges from approximately 1,070 psi to approximately10,000 psi.
 9. The processing system of claim 1, wherein saidsupercritical fluid includes supercritical carbon dioxide (CO2).
 10. Theprocessing system of claim 1, wherein said means includes a valveconnected to the inlet of the chamber to regulate the pressure to alimited gradient below the chamber pressure during fill and filledconditions.
 11. A vacuum chuck assembly for a high pressure fluidprocessing system for processing a substrate in a chamber, the assemblycomprising: a platen having a wafer supporting surface and configured tosupport said substrate on said surface for high pressure fluidprocessing; one or more fluid channels in said platen coupled to saidwafer supporting surface; a clamping fluid control system including aclamping fluid line, a first pressure-limiting valve, a secondpressure-limiting valve and a third pressure-limiting valve; saidclamping fluid line being: coupled to said channels, coupled to theoutlet of a first pressure-limiting valve that is operable to maintainthe pressure in said clamping fluid line to not less than a firstmaximum pressure gradient less than the pressure in said chamber, andcoupled to the inlet of a second pressure-limiting valve that isoperable to maintain the pressure in said clamping fluid line to notmore than a second maximum pressure gradient more than the pressure toan exhaust line that is coupled to said chamber; and said thirdpressure-limiting valve: having an inlet coupled to said chamber, havingan outlet coupled to said exhaust line, and being operable to maintainthe pressure in said exhaust line at a pressure that is not less than athird maximum pressure gradient less than the pressure in said chamber,said third maximum pressure gradient being greater than said secondmaximum pressure gradient.
 12. The vacuum chuck assembly of claim 11wherein: said first maximum pressure gradient is greater than thedifference between said third maximum pressure gradient and said secondmaximum pressure gradient.
 13. The vacuum chuck assembly of claim 11wherein: said first maximum pressure gradient is not more than a maximumclamping pressure by which said chuck holds said substrate against saidplaten.
 14. The vacuum chuck assembly of claim 11 wherein: said thirdmaximum pressure gradient is less than said second maximum pressuregradient by at least a minimum clamping pressure by which said chuckholds said substrate against said platen.
 15. The vacuum chuck assemblyof claim 11 further comprising: a vacuum pump connected to said clampingfluid line to maintain a minimum clamping pressure by which said chuckholds said substrate against said platen.
 16. The vacuum chuck assemblyof claim 11 wherein: said first maximum pressure gradient is greaterthan the difference between said third maximum pressure gradient andsaid second maximum pressure gradient; said first maximum pressuregradient is not more than a maximum clamping pressure by which saidchuck holds said substrate against said platen; said third maximumpressure gradient is less than said second maximum pressure gradient byat least a minimum clamping pressure by which said chuck holds saidsubstrate against said platen; and said assembly further comprises avacuum pump connected to said clamping fluid line to maintain saidminimum clamping pressure.
 17. A method of controlling fluid clampingpressure to the backside of a substrate on a platen of a pressure biasedwafer holder in a high pressure processing chamber, the methodcomprising: filling the processing chamber with processing fluid to ahigh processing pressure; applying a clamping fluid to the backside of asubstrate on a platen in said processing chamber at a backside pressurethat is responsive to frontside pressure exerted by said fluid on saidsubstrate, such that said backside pressure is less than the frontsidepressure by not more than a maximum clamping pressure gradient.
 18. Themethod of claim 17 further comprising: maintaining said backsidepressure at not less than a minimum clamping pressure gradient belowsaid frontside pressure.
 19. The method of claim 18 wherein: saidfilling includes applying said clamping fluid to said platen from fluidbeing supplied to said processing chamber through a biased check valvethat is set to establish said maximum clamping pressure gradient; andsaid maintaining includes removing said fluid from said chamber and saidclamping fluid from said platen through one or more biased check valvesthat are set to establish said minimum clamping pressure gradient. 20.The method of claim 17 wherein: said filling includes applying saidclamping fluid to said platen from fluid being supplied to saidprocessing chamber through a biased check valve that is set to establishsaid maximum clamping pressure gradient.